A conventional appliance for drying articles such as a clothes dryer (or laundry dryer) for drying clothing articles typically includes a cabinet having a rotating drum for tumbling clothes and laundry articles therein. One or more heating elements heat air prior to the air entering the drum, and the warm air is circulated through the drum as the clothes are tumbled to remove moisture from laundry articles in the drum. Gas or electric heating elements may be used to heat the air that is circulated through the drum.
In a known operation, ambient air from outside is drawn into the cabinet and passed through the heater before being fed to the drum. Moisture from the clothing is transferred to the air passing through the drum. Typically, this moisture laden air is then transported away from the dryer by, for example, a duct leading outside of the structure or room where the dryer is placed. The exhausted air removes moisture from the dryer and the clothes are dried as the process is continued by drawing in more ambient air.
Unfortunately, for the conventional dryer described above, the exhausted air is still relatively warm while the ambient air drawn into the dryer must be heated. This process is relatively inefficient because heat energy in the exhausted air is lost and additional energy must be provided to heat more ambient air. More specifically, the ambient air drawn into the dryer is heated to promote the liberation of the moisture out of the laundry. This air, containing moisture from the laundry, is then exhausted into the environment along with much of the heat energy that was used to raise its temperature from ambient conditions.
One alternative to a conventional dryer as described above is a heat pump dryer. More specifically, a heat pump dryer uses a refrigerant cycle to both provide hot air to the dryer and to condense water vapor in air coming from the dryer. Since the moisture content in the air from the dryer is reduced by condensation over the evaporator, this same air can be reheated again using the condenser and then passed through the dryer again to remove more moisture. Moreover, since the air is recycled through the dryer in a closed loop rather than being ejected to the environment, the heat pump dryer can be more efficient to operate than the traditional dryer described above. In addition, the heating source provided by the sealed refrigerant system of a heat pump dryer can be more efficient than a gas or electric heater implemented in the conventional dryer.
In typical heat pump dryer systems, the closed loop of air is substantially sealed from the ambient environment (e.g., an internal volume defined by the cabinet of the dryer appliance). During operation of a typical heat pump dryer, as air circulates, the temperature of the air within the sealed loop increases. Similarly, the thermal load to the sealed refrigerant system increases. In some instances, the compressor of the sealed refrigeration system may be unable to handle the increased thermal load and overheat (e.g., at a compressor portion) due to the compressor discharge temperature exceeding an upper operating limit.
In addition to potential issues with overheating, typical heat pump dryers require significantly higher cycle times when compared to other conventional systems. In other words, the time required to dry a given load will often be much higher for a heat pump dryer when compared to a conventional gas or electric dryer appliance.
Accordingly, a dryer appliance having improved efficiency over conventional gas or electric dryers, as well as typical heat pump dryers would be advantageous. In particular, a dryer appliance that further reduced cycle times over typical heat pump dryers would be useful.